With ballots set, Texas political landscape could be...

1of2Senator Ted Cruz talks to the media down the street from the First Baptist Church of Sutherland Springs, Monday afternoon, Nov. 6, 2017.Photo: Mark Mulligan, Mark Mulligan / Houston Chronicle

2of2Rep. Beto O'Rourke, D-Texas, speaks to reporters during a campaign stop in his bid for a U.S. Senate seat on Sunday, April 2, 2017, in Houston. The little-known El Paso congressman, 44, announced Friday that he is challenging incumbent Sen. Ted Cruz, R-Texas, in 2018, in an uphill battle in a state that has no elected a Democrat statewide since 1994. ( Brett Coomer / Houston Chronicle )Photo: Brett Coomer, Staff

WASHINGTON – The first Texas congressional elections in the Donald Trump-era could be among the state's most tumultuous, with a bevy of seats coming open in 2018 while U.S. Rep. Beto O'Rourke challenges incumbent Sen. Ted Cruz in a new test of Democratic strength in the Lone Star State.

But before O'Rourke can take on Cruz in November, he'll first have to get past a last-minute Democratic primary challenge from Houston-area resident Edward Kimbrough, who filed late Monday.

Another marquee contest will center on Houston, where nine-term Republican John Culberson, representing one of only three Texas congressional districts won by Hillary Clinton last year, will face off next November against the top vote-getter in an energized group of Democratic primary contenders.

Two of them, non-profit executive Alex Triantaphyllis and attorney Lizzie Fletcher, each has outpaced recent fundraising efforts by Culberson, who has become a top target in Democratic hopes of winning back the House.

As state election filings closed on Monday, no less than five Democrats are vying for Culberson's seat, including Houston physican Jason Westin, anti-Trump activist Laura Moser, and assistant city attorney James Cargas, now making his fourth bid in the 7th congressional district.

Cargas garnered 44 percent of the vote in 2016, the best showing by any Democrat in the affluent west Harris County district since 1964.

A recent survey by the Democratic-leaning Public Policy Polling firm found Culberson with an approval rating of 31 percent, lower than President Donald Trump's 37 percent in the district.

Moreover, 55 percent of voters said they disapprove of the way Culberson is doing his job, while 54 percent disapprove of the current GOP tax proposal which will likely be the centerpiece of his campaign.

Those percentages, along with Culberson losing a hypothetical matchup against a "Democratic opponent" 39 percent to 49 percent, indicate that Culberson could be vulnerable in 2018.

Democrats also are targeting a perennial battleground district along the border in west Texas, where two-term Republican Will Hurd of San Antonio will face one of at least four Democratic primary challengers, the most talked about being former federal prosecutor Jay Hulings.

Two other Democrats, both from San Antonio, filed to challenge Hurd: former Air Force intelligence officer Gina Ortiz Jones; and Rick Trevino, who taught high school history until recently.

A strong Democratic challenge in either the Senate race or Texas' two most competitive congressional districts could put the state back in the national spotlight for the first time since an 11-hour filibuster propelled Democratic state Sen. Wendy Davis into the 2014 governor's race against Republican Greg Abbott, who prevailed in a landslide.

At least one other incumbent will be in the spotlight in the March 6 primary: Corpus Christi Republican Blake Farenthold, who recently acknowledged that he benefited from a special federal fund to cover a confidential $84,000 settlement stemming from a 2014 sexual harassment suit.

Farenthold, elected in 2010 in a Tea Party wave, has continued to deny any wrongdoing – and vowed to repay the government. But the House Ethics Committee announced last week that it would extend a probe into the case, which was brought by his former spokeswoman.

Meanwhile, five Republicans have filed primary challenges against Farenthold in what remains a GOP stronghold. The latest candidate to jump in the race was Bech Bruun, the former chairman of the Texas Water Development Board who is from Corpus Christ but lives in Austin.

Earlier last week Republicans Jerry Hall, Eddie Gassman and Christopher K. Mapp all qualified for the primary as well. Entering the race earlier was former Victoria County Republican Party chairman Michael Cloud.

Two Democrats have also jumped in: Raul (Roy) Barrera of Corpus Christi and Ronnie McDonald of Bastrop.

Several other Republican primary elections, normally quiet affairs in a deep "red" state represented by entrenched incumbents, promise to be lively in 2018.

That is owing to a wave of congressional retirements, including the exit-under-pressure of Arlington Republican Joe Barton, who made national headlines recently for a viral nude picture he acknowledged sending to a woman he was seeing before the end of his second marriage.

The departure of Barton, Texas' longest-serving congressman, opened up a floodgate of GOP hopefuls in what is still considered a solid Republican district. Among them: Tarrant County Tax Assessor-Collector Ron Wright, and Jake Ellzey, a retired Naval combat pilot and a member of the Texas Veterans Commission.

Three other veteran Republicans also are headed for the exits, including two powerful committee chairmen: San Antonio's Lamar Smith, chairman of the House Science Committee, and Dallas' Jeb Hensarling, who presides over the House Financial Services Committee.

The retirement of Smith, who has held his sprawling, San Antonio-based seat for three decades, brought an outpouring of GOP interest, including from former congressman Francisco "Quico" Canseco.

At Monday's candidate filing deadline, former Bexar County GOP chairman Robert Stovall and state Rep. Jason Isaac, of Dripping Springs, were among a growing field of Republican candidates.Stovall said that he had installed phones in a campaign office on Monday while concentrating on raising money. He said he believes that he can raise $600,000 for the campaign and held out hopes of approaching $1 million.

"Fundraising for campaigns is always challenge, but the good thing is that as chairman, I got to know a lot of the heavy-hitters in our county and beyond. So I think the doors will be a little bit easier to open," he said.

Among candidates filing for the Democratic nomination in Smith's district, Austin Entrepreneur Joseph Kopser has been far ahead in fundraising, a potential advantage in a district where television advertising is expensive.

By late Monday, at least six Republicans and one Democrat had filed to replace Hensarling.

The retirement of former Vietnam POW Sam Johnson of Plano also will likely bring a fresh Republican face to Congress next year, further altering the contours of the Lone Star State's political landscape. Republican Van Taylor and two Democrats had filed by Monday, including Plano attorney Sam Johnson, no known relation to the incumbent.

Houston seats

Back in Houston, two more heavily-gerrymandered congressional seats are changing hands due to retirement, one Republican and one Democrat.

In the 2nd Congressional District, nine Republicans filed to run in a March 6 primary with hopes for replacing GOP U.S. Rep. Ted Poe of Humble, who announced earlier this year he's retiring after seven terms in the U.S. House. Five Democrats also filed to battle in the Democratic primary for a suburban district that Poe won easily in 2016 by more than 17 percentage points.

Almost all of the candidates in both parties are neophytes to elective office. The only candidate in the race who has previously won any election is state Rep. Kevin Roberts, a Republican who has represented northwest Houston in the state Legislature since January.

"I'm the only one who has run and won," Roberts said. "And I have a voting record where people can see what I've accomplished."

The retirement of U.S. Rep. Gene Green after 13 terms in Congress has produced another large field with five Democrats certain to be on the March 6 ballot in the bid to replace him in a largely eastern Houston and Harris County seat.

Longtime Democratic strategist Marc Campos said State Sen. Sylvia Garcia, a Houston Democrat, has emerged as a favorite after several other key Democrats took a pass on the race. While Garcia is the only candidate in the race who has held office before, her opponents are all promising to campaign as new blood in politics.

Attorney Roel Garcia, who is also running for the 29th Congressional seat, said he'll stress he's not a career politician on the campaign trail and offers real change. Besides those two, the race includes real estate agent Dominique Garcia, teacher Hector Morales, and Beaumont businessman Tahir Javed. On the Republican side Phillip Aronoff and Robert Schafranek will compete in the GOP primary.